Proteins are necessary for tissue repair and for the construction of new tissue. Every cell needs protein to maintain its life. Protein is also the primary substance used to replace worn out or dead cells. Your muscles, hair, nails, skin, and eyes are made of protein.
Taking supplemental chromium has been shown repeatedly to improve insulin sensitivity and glucose tolerance, even to the point of reversing type II diabetes in many people (1). Thus, as my old clinical nutrition professor pointed out, apparently a chromium deficiency can actually lead to type II diabetes.
Since exercise-induced increases in insulin sensitivity are in part driven by increased reactive oxygen species production (ROS)[1], a study in 2009 by Ristow et al, examined the effects of supplementation with vitamin C (500mg twice/day) and vitamin E (400IU/day) on changes in insulin sensitivity caused by exercise.